The invention involves a device for transferring toner from imaging members or photoconductors.
In electrophotography and other imaging technologies, toner or toner material is transferred from a locally charged imaging member or photoconductor drum to the printed material. The term imaging member is understood to be any type of medium from which toner is transferred to a final printed material, for example, an imaging drum. The efficiency of the toner material transfer is, for the exclusive application of pressure on the printed material without additional arrangements, approximately 80%, i.e. 80% of the toner material that is adhering to the imaging member due to electrostatic forces is rolled off onto the printed material.
In the prior art, in order to increase the toner material transfer, a static d.c. voltage has been applied in the area between the printed material and the imaging member, which, in addition to the transfer of the toner material through mechanical pressure, exerts electric forces on the electrically charged toner material and increases the portion of the toner material that adheres to the printed material. Problematic in the application of a suitably strong static electric field is the danger of electric arc-over and breakdown of the static electric field, so that the size of the static electric field is limited.
Using the measure of a static electric field, approximately 90% of the toner material originally located on the imaging member prior to roll-off is removed from the imaging member. The remaining portion of approximately 10% of the toner material represents a disturbance for the subsequent imaging of the imaging member and is thus undesirable. The remaining toner material is removed in a different manner, either using a brush that acts upon the imaging member or a vacuum evacuation device. The material expense and cost for these measures for removing toner material is considerable.
Accordingly, the purpose of this invention is to improve the effective transfer of toner material from an imaging member to the printed material. This is achieved using a process and a device for transferring toner from an imaging member to printed material using a d.c. voltage in the area between the imaging member and the printed material, whereby the d.c. voltage is at least temporarily combined with a transient (ripple) a.c. voltage. By this characteristic the efficiency of the transfer of toner material is improved considerably.
The invention and its advantages will be better understood from the ensuing detailed description of preferred embodiments, reference being made to the accompanying drawings in which like reference characters denote like parts.